Yes, my feeling was that Sidebottom extrapolated an Anglian mythology from the Norse, about which we know more, and it does seem likely that they would have had much in common.I didn't mind Harry Sidebottom drawing on Norse mythology for Ballista's beliefs; there's not much else, and he might as well start somewhere
Despite my complaint that Beowulf is more recent than Ballista, the piece of poetry was a brilliant choice, I thought, mixing the symbolic imagery of the Germanic raven and that of the Roman eagle, with the wolf being significant to both. Ballista is part of both cultures, though when under stress he does tend to call on the Allfather rather than Jupiter I think I remember seeing somewhere an opinion that Beowulf the poem originally had elements of Anglian dialect, though might be wrong on that.
"The dark raven shall have its say
And tell the eagle how it fared at the feast
When, competing with the wolf, it laid bare the bones of corpses"
Beowulf Lines 3021-27 (following Beowulf's death)
I wondered if Sidebottom might be a Tolkien fan? Ballista's given Germanic name is Dernhelm, the name Eowyn takes when she fights as a warrior in the army of Rohan.
Anyway, nitpicking aside, Fire in the East is a great read and I can see I'll be kept quiet for some time chasing up the rest in the series!